The present invention relates to an image forming apparatus that fixes a toner image transferred to a sheet to the sheet by thermocompression bonding, more particularly, to a technology that discharges heat generated in an apparatus to an outside of the apparatus.
In an image forming apparatus that fixes a toner image transferred to a sheet to the sheet by thermocompression bonding, during a printing period, the sheet is heated to one hundred and tens of degrees by a fixing device, so that the toner forming the toner image is melted and the toner image is fixed to the sheet. Because of this, high-temperature heat, which is generated from the fixing device during a continuous sheet feeding period, stays in the apparatus.
FIG. 14 is a left side sectional view showing a structure near a conventional fixing device. A duct frame 55, which is mounted between two side plates (not shown) disposed to oppose each other and a lower surface is opened, is disposed right over a fixing device 9. The fixing device 9 includes a heat roller 9a heated by a heater and a pressure roller 9b pressed against the heat roller 9a. High-temperature heat 100 generated from the fixing device 9 moves to an upper inner surface 55a of the duct frame 55 and goes to a state to stay in the duct frame 55. Because of this, the duct frame 55 must be composed of a heat-resistant resin to prevent the duct frame 55 from being deformed by the heat, which is a cause of cost increase. To solve this problem, for example, an image forming apparatus is already proposed, in which a fan 60 is disposed right before a sheet delivery portion 50 that delivers a sheet, on which a toner image is fixed, to outside; and the high-temperature heat generated from the fixing device 9 is discharged to the outside of the apparatus to cool an inside of the apparatus.
According to the conventional image forming apparatus described above, there is a problem that indeed the heat moving to a downstream side beyond the fixing device in a conveyance direction is discharged to the outside of the apparatus; but the heat moving to an upstream side beyond the fixing device 9 in the conveyance direction stays in the apparatus. If the heat stays in the apparatus, the apparatus is likely to fall into a malfunction state. Besides, it becomes essential to dispose a fan; accordingly, the cost increases. Further, also electric power for operating the fan and the operation sound become problems.